var items = [{
    id: 1,
    title: '项目1',
    children: [
        {
            id: 11,
            title: '项目1-1'
        }, {
            id: 12,
            title: '项目1-2'
        }
    ]
}, {
    id: 2,
    title: '项目2',
    children: [
        {
            id: 21,
            title: '项目2-1'
        }, {
            id: 12,
            title: '项目2-2'
        }
    ]
}, {
    id: 3,
    title: '项目3',
    children: [
        {
            id: 21,
            title: '项目3-1'
        }, {
            id: 12,
            title: '项目3-2'
        }
    ]
}]